1. Field of the Invention
The invention relates to methods and apparatus for dispensing medication at a surgical site. More particularly, the invention relates to methods and apparatus for dispensing antibiotics at an orthopaedic surgical site.
2. Brief Description of the Related Art
In open surgical procedures, it is common to apply an antibiotic, analgesic, growth stimulator, or other chemical agent at the surgical site prior to closing the incision in order to control infection, decrease pain, promote growth, etc.
One of the most devastating complications of total joint arthroplasty is deep sepsis. Treatment of an infected joint replacement is difficult due to its location, and localized devascularization resulting from this procedure.
Current approaches to therapy for deep infections include systemic or parenteral antibiotic regimes, and the use of antibiotic impregnated acrylic bone cement. Due to the localized devascularization it is difficult to achieve therapeutic levels in the bone surrounding the implant without exceeding toxic serum concentrations when utilizing systemic or parenteral treatments. The use of antibiotic containing bone cement results in high local concentrations, while avoiding toxic serum levels, but the antibiotic has been shown to elute in trace quantities for extended periods of time (greater than one year). Residual trace amounts of antibiotics have raised concerns of resistant strain formation. An additional concern regarding adding antibiotics to bone cement is the possible degradation of mechanical properties of the bone cement whose primary function is as a fixation material.
According to the state of the art, it is preferable to apply therapeutic concentrations at the surgical site for a period of 7 to 10 days, with no residual antibiotics lingering for extended periods of time. It is also desirable to achieve these high local concentrations without elevating serum concentrations, thus reducing the threat of systemic toxicity. A means of antibiotic treatment that can be utilized for joint replacement procedures that either involve the use of bone cement or not is desirable as well.
U.S. Pat. No. 5,681,289 to Wilcox et al. discloses a dispensing bladder for passing a low volume flow of a liquid chemical agent at an orthopaedic surgical site. The bladder is installed adjacent to or as part of an orthopaedic implant. It is coupled to a tube which receives a supply of liquid chemical such as an antibiotic via an injection port or an implanted or external reservoir and pump.
The bladder may be biodegradable so as to avoid the need for extensive surgery to remove it. However, the tube, injection site, pump, and reservoir must be surgically removed. Moreover, it is believed that the delivery of a liquid antibiotic in the femoral canal may degrade the mechanical properties of bone cement on an implant stem.